At present, a fuel cell for mobile use is under development, and an appropriate air pump for supplying air to a cell of the fuel cell does not exist. It is required that the air pump of this kind has the following characteristics: supplied air does not include impurities such as oil, i.e., the air pump is of an oilless mechanism, an amount of supplied air may be relatively small flow rate of about 5 L/min to 10 L/min, but in order to overcome a pressure loss generated in an air passage of the cell of the fuel cell and to send air, it is necessary that the pressure ΔP is equal to 5 kPa, a diameter of the air pump is about φ30 mm or less because the air pump must be incorporated in a mobile device, and noise level is low.
As an air pump which satisfies these characteristics, a vane rotary type air pump seems to be admissible. A conventional vane rotary type pump will be explained with reference to FIGS. 8 and 9.
In a conventional vane rotary type vacuum pump of this kind, a cylindrical rotor 2 is disposed in a cylinder 1 having a cylindrical inner surface, a center axis of the rotor 2 is separated from a center axis of the cylinder 1 by a predetermined amount, a plurality of vane grooves 3 are provided in the rotor 2 in a direction of the center axis thereof, plate-like vanes 4 are slidably fitted in the vane grooves 3, and tip ends of the vanes 4 contact with and slide on the inner surface of the cylinder 1. An open end of each of the vane grooves 3 is located in a region in a rotation direction of the rotor 2 with respect to a straight line connecting a center of the rotor 2 and a closed end of that vane groove 3. That is, the vane grooves 3 are inclined in the rotation direction, and when the rotor 2 rotates, tip ends of the vanes 4 contact with and slides on the inner surface of the cylinder in a “scooping” positional relation (see patent document 1 for example).
Alternately, the vane grooves 3 are disposed radially from the center axis of the rotor 2 (see patent document 2 for example).
[Patent Document 1] Japanese Patent Application Laid-open No. S62-276291
[Patent Document 2] Japanese Utility model Application Laid-open No. S56-83688